Finger/stylus touch pad

ABSTRACT

A touch pad module to implement user input functions to an electronic device. The touch pad module includes a sensor layer which, when used in conjunction with an insulative layer and contiguous conductive layer enable the touch pad module to sense both finger and stylus input data to the electronic device.

TECHNICAL FIELD OF THE INVENTION

The present invention involves a touch pad module for use with anelectronic device, such as a notebook computer, which makes use of suchmodules to implement user input functions. The touch pad module isconfigured of certain insulative and conductive layers as to enable theelectronic device to sense input data from both finger and stylus.

BACKGROUND OF THE INVENTION

Over the last several years, capacitive touch pad pointing devices haveentered widespread use in personal computers. There are at least threedistinct capacitive sensing technologies used in touch pad devicestoday:

-   -   1. The “Field Distortion” approach, used by Cirque and Alps as        described in PCT Application No. US90/04584, Publication No.        WO91/03039 to Gerpheide. Specifically, Gerpheide teaches the        application of an oscillating potential of a given frequency and        phase to all electrodes on one side of a virtual dipole, and an        oscillating potential of the same frequency and opposite phase        to those on the other side. Electronic circuits develop a        “balanced signal” which is zero when no finger is present, and        which has the polarity of a finger on one side of the center of        the virtual dipole, and the opposite polarity of the finger on        the opposite side. To characterize the position of the finger        initially, the virtual dipole is scanned sequentially across the        tablet. Once the finger is located, it is “tracked” by moving        the virtual dipole toward the finger once the finger has moved        more than a row or column of the matrix constituting the        capacitive sensor touch pad. Because the virtual dipole method        operates by generating a balance signal that is zero when the        capacitance does not vary with distance, it only senses the        perimeter of the finger contact area, rather than the entire        contact area.    -   2. The charge-detection approach used by the present assignee        described in its U.S. Pat. No. 5,374,787 to Miller et al.        Specifically, the present assignee employs what is called a        “finger pointer” technique. This approach is to provide a        position sensing system including a position sensing transducer        comprising a touch-sensitive surface disposed on a substrate,        such as a printed circuit board, including a matrix of        conductive lines. A first set of conductive lines runs in a        first direction and is insulated from the a second set of        conductive lines running in a second direction generally        perpendicular to the first direction. An insulating layer is        disposed over the first and second sets of conductive lines. The        insulative layer is thin enough to promote significant        capacitive coupling between a finger placed on its surface and        the first and second sets of conductive lines. Sensing        electrodes respond to the proximity of a finger to translate the        capacitance changes of the conductors caused by the finger        proximity into position and touch pressure information.    -   3. An unrelated approach employed currently by Logitech.

All three of these technologies share an important common feature: Thefinger is detected by a plurality of horizontally-aligned sensorelectrodes disposed on a first layer, separated by an insulator from aplurality of vertically-aligned sensor electrodes disposed on a secondlayer. Such sensor electrodes are often formed as, but are not limitedto, standard copper printed circuit board traces.

An example of such an electrode arrangement is shown in FIG. 1.Specifically, reference is made to FIGS. 1A through D, top, bottom,composite and cross-sectional views, respectively. Sensor array 10 isprovided comprising substrate 12 including a set of first conductivetraces 14 disposed on top of surface 16 thereof and run in a firstdirection to comprise row positions of sensor array 10. The set ofsecond conductive traces 18 are disposed on a bottom surface 20 thereofand run in a second direction preferably orthogonal to the firstdirection to form the column positions of the sensor array 10. The setof first and second conductive traces 14 and 18 are alternately incontact with periodic sense pads 22 comprising enlarged areas, shown asdiamonds in FIGS. 1A-1C. While sense pads 22 are shown as diamonds inFIGS. 1A-1C, any shapes such as circles, which allows close packing thesense pads 22 is equivalent for purposes of this discussion.

It is well recognized that capacitive touch pads, such as thosedescribed above, work well with fingers, but are normally unable tosense a pen or stylus. Capacitive touch pads are typically used aspointing devices. Resistive touch pads work well with pens, but requirean uncomfortable amount of pressure when used with fingers. Resistivetouch pads are typically used as writing or drawing input devices. Todate, there has not been a practical touch pad which would work wellwith both fingers and pens along with a single input device to serveboth functions. Such a touch pad would be especially valuable inportable applications where space is at a premium.

It is thus an object of the present invention to provide an input devicein the form of a touch pad module which will accept both finger andstylus input, that is, having the desirable attributes of both acapacitive touch pad for finer input and a resistive touch pad forstylus input in the same module.

This and further objects will be more readily apparent when consideringthe following disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention is directed to a touch pad module to implementuser input functions to an electronic device. The module comprises asensor layer having a length and width for detecting position of aconductive object in contact with a touch pad module. An insulativelayer is positioned over and contiguous with the sensor layer and amoderately conductive layer is positioned over and contiguous with theinsulative layer to provide a touch pad module which can be used as bothcapacitive and resistive elements have been employed in the past toreceive input information from both a finger conductive stylus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1D are top plan and side views of capacitive touch padsof the prior art.

FIGS. 2A and B show, in perspective, the effect of a finger contacting acapacitive touch pad module and a graph illustrating capacitance versushorizontal position on the pad.

FIGS. 3A and B show a depiction, in plan view, and in graphical form, ofthe measurement of finger capacitance in one dimension and thecapacitance of various electrodes based upon finger pressure.

FIGS. 4A and B show, in perspective, and in graphical form, the effectof a stylus on a capacitive touch pad module and the capacitancegenerated as a result.

FIGS. 5A and B are similar to the depictions shown in FIGS. 4A and Bwith the contact area of the stylus enlarged.

FIGS. 6A and B show, in perspective, a stylus used in conjunction withthe touch pad module of the present invention and a capacitance graphgenerated as a result.

FIGS. 7A and B illustrate in perspective, and in graphical form, theresults of the application of a stylus to a touch pad wherein theconductance of its top surface is too high.

FIGS. 8A and B illustrate in perspective, and in graphical form, theresults of the application of a stylus to a touch pad wherein theconductance of its top surface is too low.

FIGS. 9A and B are similar to FIGS. 8A and B with a finger employed inplace of the conductive stylus.

FIGS. 10A and B are again similar to FIGS. 8A and B showing the boundaryeffects of the conductive stylus contacting the touch pad module of thepresent invention near its periphery.

FIG. 11 is the touch pad module of the present invention in perspectiveshowing the embodiment of providing the user with visual feedbackcreated by the application of suitable stylus.

FIG. 12 is a graph of capacitance versus time showing the distinguishingcharacteristics between the use of stylus and finger in discriminatingthese two objects in providing positional input data to a suitableelectronic device in using the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves a touch pad module for use with anelectronic apparatus which makes use of such a module to implement allor part of its user input functions. Notebook and desktop computers aswell as copiers are typical examples of such electronic apparatus havingneed for a touch pad device such as that disclosed herein. When used inconjunction with a computer, a touch pad allows the user to manipulate agraphics cursor on a CRT display or allows a user to manipulate a stylusthereby allowing input of written text. The touch pad comprises asensitive planar surface and a means for detecting the position of anobject, such as a finger or stylus, near or in contact with thesensitive planar surface. The touch pad continuously communicates thisposition information to the electronic apparatus typically at a rate offrom 40 to 100 Hz.

As noted previously, the touch pad module of the present invention canbe used to implement user input functions to an electronic devicethrough the use of both the finger of a user as well as through the useof a conductive stylus held by the user. FIG. 2 shows the effect of afinger on a sensor of the prior art, that is, capacitive sensor intendedto accept positional data by the application of a fingertip to the touchpad module. Above the electrodes 202 is an insulating layer 201 whichprovides the surface 203 over which the finger 204 is detected (see FIG.2A). In operation, each electrode on electrode layer 202 provides oneplate of a capacitor and the finger 204, if present, provides a secondplate, with the insulating layer 201 forming the dielectric betweenthem. The conductance of the human body, combined with the human body'sinherent capacitance to free space, causes the finger to appear to beelectrically grounded in terms of its capacitance to the electrodes.Sensing electrodes scan the array of electrodes for increasedcapacitance to ground caused by the presence of a finger or other objectover them. By measuring the capacitance on both the horizontal and thevertical electrodes, the location of the finger can be determined.

FIG. 2B shows a graph of capacitance versus horizontal position on thepad. The capacitance is proportional to the finger's circular area ofcontact. Hence, the capacitance is highest near the center of the fingerand tapers off toward the edge of the region of contact. Away from thefinger, the capacitance is essentially zero, i.e., unaffected by thefinger. Touch pads measure the finger position by locating the peak 206of the curve 205 in FIG. 2B.

The position of the finger can be determined much more accurately thanthe distance between the electrodes if the finger is wide enough toprovide a measurable signal on more than one of the electrodes in eachof the horizontal and vertical dimensions. FIG. 3 shows the effects offingers of various sizes on the electrode matrix. For simplicity,electrode grid 351 is shown in just the horizontal dimension, and theelectrodes are shown as linear wires when, in fact, a more complexpattern such as linear strings of diamond shapes may be preferred inpractice. The finger (not shown) makes an approximately circular area ofcontact with the surface. This circular region 352 is typically largeenough to cover several adjacent electrodes. The capacitance on anelectrode is proportional to the area of the electrode that is coveredby the finger. This area of overlap is largest near the center of thefinger, and tapers off toward the edge of the finger contact region.FIG. 3B shows graph 355 of the capacitances of the various electrodes.The capacitance 356 of the electrode nearest the center of the finger ishighest because that electrode has the greatest overlap with the finger.Because the finger is large compared to the electrode spacing, theadjacent electrodes sense a reduced but non-zero capacitance. Therelative magnitudes of the detected capacitances on the nearbyelectrodes can be used to determine the position of the fingeraccurately with sub-electrode resolution. One popular method computesthe centroid of the entire curve 355; another method finds the electrodewith maximum capacitance and interpolates using a quadratic fit to theadjacent electrode readings.

If finger 353 is narrower than the distance between electrodes, then itmay produce a signal on just one electrode 357 and high-resolutioninterpolation is impossible. If the finger 354 is extremely narrow, itmay fall entirely between electrodes and not register at all as shown at358. Fortunately, real fingers are wide enough to allow for goodinterpolation with a touch pad having a feasible number of electrodes(e.g., 15 electrodes in each dimension).

To use a stylus with such a capacitive sensing touch pad, the stylusmust have certain special properties. First, the stylus must beconductive so as to form the required second plate of detectablecapacitance. The conductive stylus is grounded either by direct contactwith the skin of the effectively grounded human, or by capacitivecoupling to the human. Suitable materials for the stylus include metals,and highly conductive plastics such as nylon loaded with carbon fibersor carbon powder.

Second, the stylus must form a large enough signal on at least twoadjacent traces in each dimension to allow for accurate positionmeasurement. Traditional stylus designs feature a pointed tip which isnot large enough to form a signal on more than one trace, as shown inFIG. 4. Stylus 301 has such a small contact area 302 that the resultingcapacitance signal 303 is both too narrow and too low in amplitude foreffective position measurement.

Several designs for a wide stylus have been attempted. For example, aball of conductive foam may be attached to the end of the stylus, or asmall circular plate of metal can be attached by a ball joint to thetip. FIG. 5 illustrates the latter design. Stylus 401 is tipped withplate 402, whose area has been chosen to mimic the contact area of atypical finger. Hence, the capacitive signal 403 created by the plate onthe electrodes is a good simulation of the signal produced by a truefinger (compare curve 403 to curve 205 of FIG. 2). Stylus designs ofthis kind have been built and shown to work, but they are too clumsy,bulky and fragile to gain wide acceptance among users.

For these reasons, the great majority of pen-actuated touch padscurrently manufactured use resistive, not capacitive, sensors. In aresistive touch pad, pressure from the finger or stylus pushes aflexible conductive membrane against another conductive surface andthereby detects a measurable electrical signal. The resistive touch padworks well with a pointed stylus, but because it requires actualpressure, the resistive pad is uncomfortable to use with a finger. Also,the large contact area of a finger reduces the accuracy of a resistivepad. Finally, because the resistive touch pad contains moving parts, itis more fragile than a capacitive touch pad. Hence, a capacitive touchpad that could work with a point-tipped stylus would be of considerablevalue in the marketplace.

As noted previously, the present invention involves placing a moderatelyconductive layer above the insulating layer, so that the groundedconductive stylus makes contact with the moderately conductive layer.The conductive layer effectively spreads out the ground image of the tipof the stylus, forming a larger second capacitor plate which can besensed by more than one electrode on each of the horizontal and verticalaxes.

In FIG. 6, electrode 503 and insulating layer 502 have been covered bymoderately conductive layer 501. Layer 501 is made from a conductivematerial durable enough to be exposed as the surface of the touch padwith no protective coating. A suitable material for this purpose isconductive carbon powder in a plastic carrier material such as epoxy. Aconductive stylus 504 is then touched to the surface. Because stylus 504is held by the human, the stylus is effectively grounded as previouslydisclosed. The tip of stylus 504 makes electrical contact withconductive layer 501, causing a grounded region 505 to form on theconductive layer. Because layer 501 is only moderately conductive, thegrounding effect dissipates with distance from the point of contact withthe stylus. A sensing circuit which measures capacitance to ground willmeasure a strong signal in region 505, but little or no signal far awayfrom region 505 and the stylus tip.

By controlling the conductivity of layer 501, the perceived image sizeof the tip of the stylus can be adjusted to provide sufficient signal onan appropriate number of electrodes. This permits the stylus 504 to beformed in any convenient size and shape, such as that of a familiarfine-tipped pen.

If the conductive layer is too conductive, then the image will be verylarge, possibly even covering the entire surface of the touch pad. Inthis case it may not be possible to determine the location of the stylusby measuring the capacitance on each electrode. In FIG. 7, layer 601 hassuch high conductance (i.e., such low resistance) that stylus 602creates a grounded region 603 that covers a large fraction of thesurface. Hence, the capacitance graph 604 is so wide that it is hard tomeasure the peak of the curve accurately. In the extreme case of ahighly conductive layer 601, contact with a stylus anywhere on thesurface would produce a uniform grounding effect over the entire surfaceand no position information could be gained.

If the conductive layer is not conductive enough, then the image willnot be much larger than the tip of the stylus, and it may not bepossible to determine the location of the stylus to a resolution anyhigher than the electrode pitch. In FIG. 8, layer 701 has such lowconductance (i.e., such high resistance) that grounded region 703 isvery small, producing a graph 704 which is not much better than graph303 with no conductive layer at all.

For best operation, the conductivity of the surface layer should bechosen such that the image of the stylus is about the same size as theimage generated by a finger on a normal capacitive sensor (note thesimilarity of capacitance graphs 205 of FIG. 2 and 506 of FIG. 6).

A key benefit of the present invention is that the touch pad can stillbe used effectively with a finger, as well as with a stylus aspreviously disclosed.

The fundamental mechanism of the capacitive touch pad as described abovecontinues to detect fingers on touch pads with the additional conductivelayer. In FIG. 9, finger 802 touches the surface and produces a groundedregion 803 which is larger than the image of a finger on a normal touchpad, but not so large as to render the resulting capacitance graph 804unusable for calculating the finger position.

Thus, the addition of a conductive layer 801 allows the touch pad towork well with either a stylus or a finger.

It was determined that when the stylus or finger nears the edge of thesensor, the present invention can cause a noticeable distortion in themeasured position. Referring to FIG. 10, stylus 902 being close to edge904 of the sensor, causes grounded region 903 to be truncated into asemicircular shape. The resulting capacitance graph shows a truncatedand lop-sided curve as seen in FIG. 10B. The true peak of the curve, andthus the true stylus position, is shown by arrow 906. The centroidmethod, if employed, will calculate a different position 905 because thecurve is truncated on one side. The simplest solution to the boundarydistortion effect is to make the touch pad somewhat larger than needed,then to cover the sensor with a bezel with a smaller opening thatprevents the finger or stylus from nearing the true edge of the sensor.

Another solution is to compensate for the distortion in later processingon the computed position data. This is possible because the effect ofthe distortion is predictable and repeatable, especially if theconductance of layer 901 is a well-controlled manufacturing variable. Tocompensate for the distortion, a stylus is placed at various positionsacross the sensor, and the corresponding measured positions tabulated.The resulting table describes a mathematical function. It is easy to seethat the effect shown in FIG. 10 produces a monotonic distortion in themeasured position, which means the tabulated function has an inversewhich can be computed by means well known in the art. The distortion iscompensated by applying this inverse function to each measured positionduring operation of the touch pad.

By choosing appropriate materials for the stylus tip and touch padsurface, the stylus can be made to leave a mark on the surface of thetouch pad, giving a visual feedback to the user. In FIG. 11, the touchpad is made of the same electrode layer 1003, insulating layer 1002, andconductive layer 1001, but conductive layer 1001 is made of a materialwhose properties cause stylus 1004 to leave a visible trail 1005 on thesurface. The material may be pliant so that the stylus leaves a groove,or have other mechanical or chemical properties that cause the stylus toleave a mark. Or, the stylus can be made of a sacrificial material suchas pencil graphite which leaves a trail when moved across the surface.With an appropriate surface material, the markings can be easily wipedoff so that subsequent marks are more easily visible.

It is possible to make materials which are both conductive andtransparent to visible light. In this case, layer 1001 may be madetransparent and layer 1002 may be made of a material which changes coloror reflectivity when mechanically disturbed. In yet another approach,all three layers 1001, 1002, and 1003 may be made transparent, and thewhole assembly placed over a display screen such as a liquid crystaldisplay (LCD) which can provide visual feedback under software control.

In some applications it may be useful to be able to distinguish betweenstylus contact and finger contact on the touch pad. Although there is noguaranteed way to make this distinction given only the capacitancegraph, it is possible to make a fairly reliable heuristic guess bynoting the differences between stylus input graph 506 and finger inputgraph 804.

The conductive layer on the touch pad surface will expand any groundedcontact by a roughly constant distance which in the preferred embodimentis comparable to the width of a finger. A stylus tip, which isessentially a point of negligible size, is expanded to be finger-sizedby the conductive layer. A finger has a finger-sized contact area, whichis expanded to a much larger size by the conductive layer. Thus, afinger can be expected to produce a grounded region of approximatelytwice the width or diameter as that of a stylus. With the diameterincreased by a factor of two, the total area of grounded contact isincreased by a factor of four. Hence, the system can measure either thetotal number of electrodes reporting increased capacitance (the diameterof the grounded region) or the total summed capacitance among all theelectrodes (the area of the grounded region) to guess whether thecontact is a stylus or a finger.

Another useful factor is that a capacitance signal produced by a fingerwill tend to fluctuate as the angle of contact of the finger on thesurface changes, but a stylus signal will remain very constant. Thestylus signal is independent of the angle at which the stylus is heldbecause the contact area of the stylus tip itself is negligible. Yetanother factor is that the stylus will produce no signal until contactis made with the surface, whereupon the signal will jump immediately tofull strength, whereas a finger will begin producing a small signal asit approaches the surface since a finger-sized conductor creates somecapacitance merely by proximity to a capacitance sensor.

FIG. 12 illustrates a graph of total summed capacitance “Z” versus time.First, a stylus contact is made which is characterized by a small,steady, sharp Z signal 1201. Then, a finger contact occurs with alarger, more varying signal 1202 with a smoother rise and fall.

In summary, the present invention recognizes, for the first time, thatthe application of a conductive layer above the insulating layer of acapacitive touch pad provides such an input device which works well withboth a finger and a conductive stylus. In addition, it is noted that thesize of the stylus tip can be made as small as desired without impactingthe ability of the touch pad to accurately determine its location.

1. A capacitive touch pad system comprising: a sensor layer; aninsulative layer disposed over said sensor layer; and a conductive touchlayer disposed over said insulative layer, wherein said sensor layer,said insulative layer and said conductive touch layer are configured toform a capacitor with a conductive object when said conductive objectcontacts said conductive touch layer, said formed capacitor having acapacitance determined in part by the conductive touch layer and theconductive object, and wherein the conductive touch layer has aconductivity configured to create an image of said conductive objectthat is larger than an area of contact of said conductive object tothereby increase the capacitance of the formed capacitor when contactingthe conductive touch layer and facilitate sensing of the capacitance todetermine a position of the conductive object.
 2. The touch pad systemof claim 1, wherein said image of said conductive object is about thesize of a finger when said area of contact is defined by a conductivestylus tip.
 3. The touch pad system of claim 1, wherein said conductivetouch layer comprises a conductive material disposed in a plasticcarrier.
 4. The touch pad system of claim 3, wherein said conductivematerial comprises carbon powder.
 5. The touch pad system of claim 1,wherein said insulative layer, said conductive touch layer and saidsensor layer are transparent, and wherein a display is positionedbeneath said sensor layer and images from the display are viewablethrough said sensor layer, said insulative layer and said conductivetouch layer, said display configured to provide visual feedback to auser of the touch pad system.
 6. The touch pad system of claim 1,further comprising: a bezel disposed over said conductive touch layerand covering a perimeter of said conductive touch layer, wherein saidbezel is configured to limit edge distortion effects by preventing theconductive object from contacting the conductive touch layer at theperimeter.
 7. The touch pad system of claim 1, wherein the touch padsystem is configured to compensate for edge distortion by use of acorrection function applied to measured conductive object positionsduring operation of the touch pad system.
 8. The touch pad system ofclaim 7 wherein the correction function is generated by measurement ofconductive object positions at multiple locations on said conductivetouch layer, tabulation of said measurements of said conductive objectpositions, and development of a mathematical function from saidtabulation.
 9. The touch pad system of claim 1, wherein the touch padsystem is configured to distinguish an identity of the conductive objectby determining a change in the capacitance over a selected time periodwhen the conductive objective is positioned proximate the conductivetouch layer, wherein the a variable change in capacitance over theselected time period corresponds to a finger determination and asubstantially constant capacitance over the selected time periodcorresponds to a stylus determination.
 10. The touch pad system of claim1 wherein the conductive touch layer is configured to produce a visualmark of the conductive object contacting said conductive touch surface.11. The touch pad system of claim 1 wherein the conductive touch layerhas the conductivity selected such that the image has an area at leastfour times larger than the area of contact of said conductive object.12. The touch pad system of claim 1, wherein the touch pad systemfurther comprises a means of distinguishing an identity of theconductive object.
 13. The touch pad system of claim 12 wherein saidmeans for distinguishing said identity of said conductive objectcomprises a means using a size of said image.
 14. The touch pad systemof claim 12 wherein said means for distinguishing said identity of saidconductive object determines a change in the capacitance over a selectedtime period when the conductive objective is positioned proximate theconductive touch layer, wherein the a variable change in capacitanceover the selected time period corresponds to a finger determination anda substantially constant capacitance over the selected time periodcorresponds to a stylus determination.
 15. The touch pad system of claim12 wherein said means for distinguishing said identity of saidconductive object comprises a means based on a rate of change of adetected change in capacitance, wherein a stylus produces an immediatefull strength detected change in capacitance upon contact with saidconductive touch layer and a finger produces a gradually increasingdetected change in capacitance as said finger approaches contacting saidconductive touch layer.
 16. A capacitive touch pad system comprising: asensor layer; an insulative layer disposed over said sensor layer; and aconductive touch layer disposed over said insulative layer, wherein saidsensor layer, said insulative layer and said conductive touch layer areconfigured to create a detectable capacitance change when a conductiveobject contacts said conductive touch layer, said detectable capacitancechange determined in part by said conductive touch layer and theconductive object, and wherein the conductive touch layer has aconductivity configured to create an image of said conductive objectthat is larger than an area of contact of said conductive object withsaid conductive touch layer to thereby increase said detectablecapacitance change when said conductive object is contacting saidconductive touch layer.
 17. The capacitive touch pad system of claim 16wherein said image of said conductive object forms a larger effectivecapacitive plate for coupling to said sensor layer.
 18. The capacitivetouch pad system of claim 16, wherein said image of said conductiveobject is about a size of a finger contact area when said area ofcontact with said conductive touch layer is defined by a tip on aconductive fine-tipped stylus.
 19. The capacitive touch pad system ofclaim 16, wherein the conductivity of said conductive touch layer isconfigured to limit a size of said image to approximately four times thearea of contact of said conductive object.
 20. The capacitive touch padsystem of claim 16, wherein said conductive touch layer is formed with aconductive material disposed in a plastic carrier.
 21. The capacitivetouch pad system of claim 20, wherein said conductive material comprisescarbon powder.
 22. The capacitive touch pad system of claim 16, whereinsaid insulative layer, said touch layer and said sensor layer are atleast partially transparent.
 23. The capacitive touch pad system ofclaim 22, further comprising: a display in operative communication belowsaid sensor layer, said display configured to be viewable through saidsensor layer, said insulative layer, and said conductive touch layer.24. The capacitive touch pad system of claim 23, wherein said display isconfigured to provide visual feedback to said user of said capacitivetouch pad system.
 25. The capacitive touch pad system of claim 16,wherein said conductive object comprises a conductive stylus holdable bysaid user such that said user is in electrical communication with saidstylus.
 26. The capacitive touch pad system of claim 16, wherein saidconductive object comprises one of a metal and a conductive plastic. 27.The capacitive touch pad system of claim 16, wherein said conductiveobject includes a conductive tip, said conductive tip selected from thegroup consisting of a wide stylus, a ball of conductive foam, and acircular metal plate with a ball joint.
 28. The capacitive touch padsystem of claim 16, wherein said conductive object comprises a finetipped conductive pen.
 29. The capacitive touch pad system of claim 16,further comprising: a bezel disposed over said conductive touch layerand covering a perimeter of said conductive touch layer, wherein saidbezel is configured to limit edge distortion effects by preventing saidconductive object from contacting said conductive touch layer at saidperimeter.
 30. The capacitive touch pad system of claim 16, wherein saidcapacitive touch pad system is configured to compensate for edgedistortion by use of a correction function applied to measuredconductive object positions during operation of said capacitive touchpad system.
 31. The capacitive touch pad system of claim 16, whereinsaid calibration means comprises: a correction function configured tocompensate for edge distortion, wherein said correction function can beapplied to measured conductive object positions during operation of thecapacitive touch pad system.
 32. The capacitive touch pad system ofclaim 16, wherein said capacitive touch pad system further comprises ameans for distinguishing an identity of said object.
 33. The capacitivetouch pad system of claim 32, wherein said means for distinguishing anidentity of said object comprises a means using a size of said image.34. The capacitive touch pad system of claim 32 wherein said means fordistinguishing said identity of said conductive object is configured todistinguish said identity of said conductive object by determining achange in said capacitance over a selected time period when saidconductive objective is positioned proximate the conductive touch layer,wherein the a variable change in capacitance over the selected timeperiod corresponds to a finger determination and a substantiallyconstant capacitance over the selected time period corresponds to astylus determination.
 35. The capacitive touch pad system of claim 32wherein said means for distinguishing said identity of said conductiveobject comprises a means based on a rate of change of a detected changein capacitance, wherein a stylus produces an immediate full strengthdetected change in capacitance upon contact with said conductive touchlayer and a finger produces a gradually increasing detected change incapacitance as said finger approaches contacting said conductive touchlayer.
 36. A capacitive touch pad system comprising: a sensor layer; aninsulative layer disposed over said sensor layer; and a conductive touchlayer disposed over said insulative layer, wherein said sensor layer,said insulative layer and said conductive touch layer are configured tocreate a detectable capacitance change when a conductive object contactssaid conductive touch layer, said detectable capacitance changedetermined in part by said conductive touch layer and said conductiveobject, and wherein said conductive touch layer has a conductivityconfigured to create an image of said conductive object that is largerthan an area of contact of said conductive object to thereby increasesaid detectable capacitance change when said conductive object iscontacting said conductive touch layer and facilitate sensing of saiddetectable capacitance change to determine a position of said conductiveobject, and wherein said conductive touch layer is configured to producea visual mark representative of said area of contact for providingvisual feedback to the user.
 37. The capacitive touch pad system ofclaim 36 wherein said visual mark is produced by a mechanical contact ofsaid conductive object with said conductive touch layer.
 38. Thecapacitive touch pad system of claim 36 wherein said visual mark isproduced by a chemical property of said conductive object.
 39. Thecapacitive touch pad system of claim 37 wherein said visual mark is analteration in at least one of a color and a reflectivity produced bysaid mechanical contact of said conductive object with said conductivetouch layer.
 40. The capacitive touch pad system of claim 37 whereinsaid visual mark is produced by a sacrificial material on a tip of saidconductive object.
 41. The capacitive touch pad system of claim 40wherein said sacrificial material comprises graphite.
 42. The capacitivetouch pad system of claim 37 wherein said conductive touch layercomprises a pliant material, and wherein visual mark is produced by agroove in said conductive touch layer in response to mechanical contactof said conductive object with said conductive touch layer.
 43. Thecapacitive touch pad system of claim 37 wherein said visual markproduced by said mechanical contact of said conductive object with saidconductive touch layer is removable.
 44. The capacitive touch pad systemof claim 36 wherein said visual mark is produced by a layer of liquidcrystal material coupled to said conductive touch layer in response tomechanical contact of said conductive object with said conductive touchlayer.
 45. A touch pad system comprising: a sensor layer; an insulativelayer disposed over said sensor layer; and a touch layer disposed oversaid insulative layer, said touch layer having a conductivity selectedto create an image of a conductive object that is larger than an area ofcontact of said conductive object, and wherein said sensor layercapacitively detects the image of said conductive object when saidconductive object is placed proximate to said touch layer, wherein theconductivity of said touch layer is configured to limit the size of saidimage to approximately four times the area of contact of said conductiveobject.
 46. A capacitive touch pad system comprising: a sensor layer; aninsulative layer disposed over said sensor layer; and a conductive touchlayer disposed over said insulative layer, wherein said sensor layer,said insulative layer and said conductive touch layer are configured toform a capacitor with a conductive object when said conductive object isplaced proximate to said sensor layer, said formed capacitor having acapacitance determined in part by the conductive touch layer and theconductive object, and wherein the conductive touch layer comprisesconductive carbon disposed in epoxy and has a conductivity selected tocreate an image of said conductive object that is at least four timeslarger than an area of contact of said conductive object to therebyincrease the capacitance of the formed capacitor when contacting saidconductive touch layer and facilitate sensing of the capacitance todetermine a position of the conductive object.